1. Field of the Invention
The present invention relates to a copy management system and, more particularly, to a copy management system including an output device embedding a specific code in an image to output the image with the embedded code and a copying device determining the specific code thus embedded in the image to control its copying process.
2. Description of the Background Art
It may be an occurrence that a confidential document, output by an output device, such as a printer, is inadvertently copied. There are a number of cases where confidential information contained in the confidential document leaks from a copied confidential document due to ease in copying. The leakage of confidential information has posed a serious social problem.
Several methods have so far been proposed to combat the problem of secret leakage. Some of the methods are proposed in Japanese patent laid-open publication Nos. 2003-101762, 2005-333359, 111161/1990 and 2004-260341. However, with these proposed methods, the means for solution may readily be detected to lead to copying of the confidential document.
The Japanese '161 publication shows a method whereby the source of leakage may readily be located in case of leakage of confidential information to outside due to copying. The disclosed method consists in a bar code representing tracking information, such as information for identifying a copying device used for copying, or copying time and/or date, and appending the bar code to the text to be copied. However, this method suffers a problem that, in copying, the bar code may be hidden or replaced by another bar code to render it difficult to detect the source of leakage to permit ready copying.
The Japanese '762 publication discloses utilizing the watermarking technique. The Japanese '359 publication discloses a method for automatically printing information on a printing person, the size of a printed matter or the printing process on the ground pattern of the printed matter in its entirety. With these printing methods, in which information on a printing person, for example, may repeatedly be embedded in the entire background of the surface of a printing paper, the information on the printing person may be sensed even though the printed matter is partially hidden or sliced out.
These printing methods are highly effective in locating the source of leakage. However, these methods do not aim at combating the leakage. It is therefore not possible with these methods to restrict the copying of a printed matter.
The Japanese '341 publication discloses a method in which a certain ground pattern is printed in the background of a confidential document. If a copying device has detected the ground pattern, it inhibits copying. With this method, the printing of a printed matter with a ground pattern is inhibited without exceptions. Hence, with this method, even a person higher in competence than a person authorized to allow for printing or a person authorized to duplicate a confidential document is unable to copy the confidential document.